It has become common practice to employ lasers in various manufacturing processes where it is necessary to remove material, such as in drilling, for example. In the fabrication of devices such as microcircuits, for example, resistor trimming is often done by utilization of a laser beam, as is material removal in the formation of circuit runs, for example.
Known lasing devices such as ruby or YAG crystals, produce a highly intense beam of coherent electromagnetic radiation. Since the crystal is of a solid cylindrical shape and since the beam of radiation exits from one end of the crystal, the beam has a substantially circular cross-sectional configuration. While a beam having such a cross-sectional shape is extremely useful for many material removal applications, it is often highly desirable that the beam have a rectangular cross-sectional shape. For example, for critical removal of material from a selected area of a microcircuit a round or elliptical beam may not prove satisfactory. One example is a memory device where fusible links are provided and where selected ones of such links must be "blown" to isolate components of the device. In such cases, a round or elliptical beam of small size may burn away a portion of a link but in doing so may damage an adjacent surface area of the device or, if extremely small, may burn away a portion of the link while still leaving portions of the link so closely adjacent to one another as to continue to permit undesirable electrical interconnection.
It has been found possible to alter the cross-sectional shape of a beam of electromagnetic radiation from round or elliptical to rectangular in many ways. This can be done electronically or optically. However, all known methods have proved undesirable for several reasons such as poor quality or definition of shape, loss of radiation energy, or uneven distribution of energy. One of the better known methods has been to direct the beam through an aperture in an opaque plate where the aperture has a configuration conforming to the desired cross-sectional shape of the beam. In this method a considerable quantity of radiation is lost because portions of the beam necessarily impinge upon and are intercepted by the opaque portions of the plate.
In a known prior art system a quasi rectangular beam shape has been created by pairs of cylindrical lens elements emitting an extreme astigmatic imaging. However, in such a system it has been found to be extremely difficult to determine before the actual material removal process where the resultant rectangular image falls. This prevents ready use of coaxial closed circuit television viewing and personal ocular viewing arrangements.